It is unexpected for ostrich or chicken egg to be single cell yet so large.
How could it happen, I thought egg is made up of several single cells.
If not, how is yolk a single cell http://www.alearned.com/egg/
Before the egg hatches, there is really only one intact cell inside the egg, that is the yolk. Before fertilization, the yolk is just an egg cell, but after fertilization, it is a fertilized egg. If the egg begins to hatch and the fertilized egg cells undergo cell division, there's not just one cell. A white spot on the surface of the yolk. The unfertilized egg is called an egg, and the fertilized egg is called a zygote, which further develops into an early blastocyst. The disc of the fertilized egg is about 3 mm in diameter, and the ovule of the unfertilized egg is smaller.